Square-wave phase modulation

Figure 20.14. Square-wave phase modulation waveform used by Drapcho et al. (Reproduced from [14], by permission of the Society for Applied Spectroscopy copyright 1997.)...

Another experimental approach is to modulate the potential of the electrode by a periodic function usually a sine or square wave and observe the synchronous spectral response by means of a phase-sensitive detector (Aylmer-... 

In practice, a sinusoidal motion of the oscillating mirror is to be preferred to the square-wave motion, and in most applications, the sinusoidal motion is used. The effects of phase modulation are the same in this case, the only difference being that the modulation factor in Eqs. (4.11) to (4.13) will be the first Bessel function 7l(2 i (ro) instead of sin(25i [Pg.116]

A square-wave modulation of 1% was then applied to the gas phase equilibrium volume, Vg. Such a small perturbation can generally satisfy the assumption of linearity. The modulation was affected by applying a current to each of the two electromagnets (Eq. 3) in turn, which moves the disc (Eq. 4) between the electromagnets rapidly (< 10 ms) and periodically. The brass bellows (Eq. 5) attached to the disc, which is part of the sorption gas... 

For the FR system with a closed volume perturbed by a square-wave, the FR parameters of the amplitude ratio Pb/Pz and the phase lag i>z-B = derived from a Fourier transformation of the volume and the pressure square-wave modulations [9,36-39]. [Pg.243]

Modulation techniques For reversible systems, a more suitable kind of method consists in using a potential modulation coupled with a phase-sensitive detection (lock-in amplifier) the potential may be modulated, for example, as a square wave between Vj and V2 and the signal from the detector may be sent to a lock-in amplifier. The signal from the lock-in provides a function A1((t) (change in intensity reaching the detector associated with the modulation), the average intensity 1(a) being measured either simultaneously or sequentially. The... 

The drift tube has several uses. It may be held at a potential of up to 500V relative to earth, and this allows us to discriminate in favour of fragment ions produced at this potential (within the drift tube) by means of the ESA. A square wave potential of up to 10V may also be applied to the drift tube this velocity modulates the ion beam and hence, through the Doppler effect, is equivalent to frequency modulation, thus allowing phase sensitive detection to be employed. 

Illustrated in Fig. 10.151, this system uses DC-to-AC conversion through phase modulation of two square wave high-frequency signals to create an output waveform. The waveform then is filtered to remove the carrier signal and feed the load. 

Cyclic Runs. Having established the inlet ratio of H2 Buta-diene for which the steady-state yield is maximised for a given residence time, the cyclic runs were carried out such that the mean value of the feed compositions were as near as possible to their optimum steady-state values. The mole fractions of H2 and Butadiene were cycled out of phase in a symmetrical square wave fashion. Such symmetrical wave forms need not be the optimum periodic operation. Indeed, Farhad Pour et al. (7 ) demonstrated theoretically that it was possible to obtain further improvement in the selectivity of series-parallel reactions in a CSTR when asymmetrical rather than symmetrical square waves are considered. Theoretically the search for the optimum wave modulation, or the number of switches over one cycle time, can be computed by search methods or optimisation routines. However, in this work we arbitrarily limited ourselves to symmetrical square waves which are 180 out of phase accepting that such a configuration may, indeed, be quite far from the optimum periodic mode. 

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